I built my own to a better spec than all of them for £700 and it will last until my daughter(s) wants to ride something else or gets bigger than 5'6" which will be a while as they are 7 and just 10.
I used a 14" OnOne Inbred, bought s/h SiD forks at 100/120mm and serviced them, fitted new deore 10spclutch mech/shifters/brakes, cassette, s/h 24" wheels initially, Sun Ringle singletrack rim, deore hubs, now have s/h Hope Hoops with Olympic rims. Got cranks made in US to 145mm (sq taper, cost me £80 incl shipping, truvativ) set up 1x10 with a 32t on 24 superstar chain guide. I still have the details if anyone wants them. OnOne flat bar cut to order, 35mm stem, superstar grips & discs. 23lb all up with pedals.
I started with the forks at 80mm using the dual air trick to lower them,and gradually have lifted them.
I may fit a 2x10 as she gets older if she needs it/we do harder stuff.
It rides great, has good geometry even with 24", it helps its a bit longer and lower than designed with 24", and obviously 26" then goes in nicely.
So it's almost a one off purchase, has really good brakes I'd be happy to ride, likewise gears and the lightest forks out there that work properly.
The geo with 24" is more suitable than some of the offerings I looked at as the standover was better for my 7yr old.
Clearly you need to have some build skills or get the kit and take it to your lbs.
I just couldn't find a std offing from anyone I was happy with.